The Siple War, also known as the Great Micronational Antarctic War was a micronational conflict between the Grand Duchy of Flandrensis, Finismund, Marie State, and the Grand Duchy of Westarctica that began on 29 January 2009 and was officially ended by Flandrensis and Finismund on 1 June 2009. The conflict gained significant notoriety in the international community was even mentioned in a Dutch travel magazine.
The conflict was sparked by a controversy over territorial claims, with both nations claiming sovereignty over Siple Island and Marie Byrd Land and neither being willing to recognize the other's claims. The nature of the conflict was later altered by the support of the Grand Unified Micronational, which lead to a massive increase in diplomatic support for Flandrensis and Finismund - despite this, GUM later withdrew its support on 27 May 2009, a few days before the conclusion of the conflict.
Hostilities between the warring nations officially came to a close on 24 September 2010 with the signing of the West-Antarctic Treaty and Westarctica joining the Antarctic Micronational Union.